Tube drawing means



3 I J. A. KOBBERUP ET AL 1 TUBE DRAWING MEANS Filed Aug. 26, 1955' Juaws' .Howara: .MThre LkeLdJ Jew in RJiObbeI' Patented Aug. 24, 1937 UNITED STATES PATENT OFFICE TUBE DRAWING MEANS Application August 26, 1935, ,Serial No. 37,906

7 Claims.

Our invention relates in general to the manufacture of tubes and has more particular reference to tubes having substantially capillary bore;

An important object of the invention is to provide for drawing a capillary tube having smooth even bore surfaces.

Another object is to provide for drawing a tube over a mandrel of hardened steel having a chromium plated drawing surface so that the product has a smooth bore surface of uniform diameter and cross-sectional shape throughout its length.

Another object is to provide for drawing a tube through a die and over a chromium placed 10 mandrel? a further object being to utilize a chromium plated carboloy or other like hard metal die for drawing tubing.

Another object is to utilize a length of piano Wire as a mandrel upon which to draw tubing 20 having a substantially capillary bore; a further object being to mount the Wire with its end extending within a drawing die whereby a tube of relatively large diameter may be drawn through the die to reduce its diameter and simultaneously 25 drawn onto and over the wire mandrel to ensure uniformity and smoothness of bore in the drawn tube; a still further object being to harden and/or chromium plate the drawing tip of the wire opposite the die to thus improve the quality and 30 uniformity of the drawn product.

Among other objects is to provide an improved easy and inexpensive method of producing uniformity and smoothness of the bore, particularly in capillary tubing; to provide an improved drawn tube of capillary bore; and to provide capillary tubing, especially of metal, having smooth uniform texture in the inner walls of the tube as well as having uniform cross-sectional area of the bore throughout the length of the tube.

40 Numerous other objects, advantages, and inherent functions of the invention will be apparent from the following description, which, taken in connection with the accompanying drawing,

discloses a preferred embodiment of the invention.

45 Referring to the drawing:

Figure 1 is a schematic view showing apparatus for-producing tubing in accordance with our invention; and v Figure 2 is an enlarged sectional view of the 50 drawing die and mandrel.

To illustrate our invention, we have shown in the drawing apparatus for the fabrication of tubing, more particularly metallic tubing having a capillary bore dimension, by drawing a rela- 55 tively larger tube simultaneously over a mandrel Y with existing practice has considerable variation in the bore throughout its length and seldom, if

'ever, and then only accidentally, is of truly circular cross-sectional shape. In precision instruments, as, for instance, where capillary tubing is utilized to carry flowing fluids, or where the a use of the tubing demands a known volume of fluid passing per unit of time through a given length of the tubing, for example, in the transmission of fluid under pressure from a temperature measuring device to a recording instrument,

such variation makes it extremely difficult to calibrate the precision instruments.

The rough unfinished bore surfaces in tubing of the sort provided heretofore is also a variant feature making the use of capillary tubing unusually laborious due to the necessity of accurately measuring and calibrating the flow characteristics of each individual length of tubing utilized. By producing tubing having bore uniformity, a standard product is achieved thus eliminating much of the labor and disadvantages heretofore encountered in the calibration and use of capillary metallic tubing.

To this end, we propose to fabricate metallic tubing by drawing the same through an opening 9 in a die H in order to compact or squeeze the tube material upon a sustaining pin or mandrel preferably comprising a length of piano wire l3 havingan end I5 disposed within the die opening 9.

The die H is or may be firmly mounted, at a drawing station, in any suitable fashion and means I l is provided for anchoring an end of the wire mandrel I3 in position such that its end I5 may extend within the die opening IS. The end 15 of the mandrel is preferably hardened and surfaced. with a finishing coat l9, preferably comprising chromium, electrolytically or otherwise plated upon the end of the mandrel. The mandrel may be detached from its anchor l1 in order to permit the same to be threaded into 5 a length of tube stock 2| having inner and outer dimensions substantially larger than the inner and outer dimensions of the finished tubing after the drawing operation. The end of the stock tube 2| may be mechanically reduced, as at 23, to permit the end of the stock tube to be inserted through the opening 9 of the die and then flattened to permit the attachment of drawing tongs 25. The mandrel I3 is then connected to the anchor l1 and the stock tube drawn through the die by advancing the drawing tongs preferably under uniform tension in the direction of the arrow in Figure 1 of the drawing.

The opening 9 in the die l9 has its narrowest dimension nearer to the die surface facing away from the anchor H, the leading edge of the opening being rounded as at 21. The trailing edge of the opening is also rounded as at 29, in order to form a conical depression 3| facing the incoming tube stock 2|. As the tube stock 2| is drawn through the opening 9, the inclined surfaces of the conical depression 3| will exert a leverage upon the walls of the tube thus causing the material of the same to be drawn inwardly, as at 33, and compacted upon the hardened end I5 of the mandrel, which thus forms a sustaining element adapted to maintain and determine the shape and size of the bore in the finished product. As the tubing is thus drawn upon ,andover the mandrel, it simultaneously passes through the portion of minimum diameter in the die opening 9, which thus determines the outside diameter of the finished tubing' The hardened end of the mandrel extends through the die and projects a sufficient distance in front of the same to support the tube during and after its passage through the die. The extreme tip of the mandrel is also preferably rounded as clearly shown in Figure 2.

-The drawn tube 35, as it leaves the extreme end of the mandrel, will have uniform smooth internal and external surfaces and the bore will be of a uniform size and cross-sectional shape,

throughout the length of the tube, corresponding to the diameter and cross-sectional configuration of the mandrel. The texture of the bore surfaces in the finished tube 35 will be substantially smooth and we believe that the smooth texture of the bore surfaces is in part provided by the chromium plated finishing layer IS on the mandrel at the place where the tubing is drawn onto and over the mandrel. We have discovered that tubing drawn on a chromium plated mandrel has unusual smoothness and uniformity in its bore surfaces.

While any suitable hard material may be used in forming the die H, we prefer to make the die of tungsten carbide and to coat the surfaces of the drawing aperture with chromium since we find that this provides a superior finish in the outersurfaces of the drawn tube.

-It will be noted that the wall thickness of the tubing is slightly reduced during passage of, the stock tube through the die. In other words, there is suificient material in the stock tube to ensure that the same, in passing through the die will be firmly pressed at all points in the circumference of the tubing upon the hardened surface of the mandrel, or sustaining member, thus ensuring a uniform cross-sectional area andsize in the bore of the finished tubing as well assmoothness in wall texture in the bore. It should be also noted that the reduction in wall thickness of the tube, during the drawing operation, will result in an extension in tube length. At the conclusion of the drawing operation, when all of the stock tube has passed through the die, it is simply necessary to sever the flattened end 23 along the line 31 and the tubing is ready for whatever use or service to which it may be desired to put the same.

It is thought that the invention and numerous of its attendant advantages will be understood from the foregoing description and it is obvious that numerous changes may be made in the form, construction, and arrangement of the several parts of the illustrated apparatus without departing from the spirit or'scope of our invention or sacrificing any of its attendant advantages, the preferred modes and forms herein described being merely for the purpose of illustrating the invention.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is as follows:

1. A die for drawing tubes comprising a block of tungsten carbide having an opening through which tubes may be drawn, the surfacesof said opening being coated with chromium.

2. Apparatus for drawing tubes comprising a die through which tubing may be drawn and a mandrel comprising a length of piano wire adapted to extend within the tubing as it passes through the die whereby to support the tubing internally, an end of said piano wire mandrel extending through the die and projecting therebeyond a distance greater than the diameter of the mandrel whereby to support the tube as and after it leaves the die.

3. Apparatus for drawing tubes comprisinga die through which tubing may be drawn, and a mandrel adapted to extend within the tubing as it passes through the die whereby to support the tubing internally, said mandrel being adapted to extend through the die and to project therebeyond a distance greaterthan the diameter of the mandrel, whereby to support the tube as and after it leaves the die, wherein the mandrel comprises piano wire having a rounded end projecting beyond the die.

4. Apparatus for drawing tubes comprising a die through which tubing may be drawn, and a mandrel adapted to extend within the tubing as it passes through the die whereby to support the tubing internally, said mandrel being adapted to extend through the die and to project therej beyond a distance greater than the diameter of the mandrel, whereby to support the tube as and after it leaves the die, wherein the mandrel comprises piano wire having its end portions chromium plated andextending in and projecting beyond the die.

5. Apparatus for drawing tubes comprising a die through which tubing may be drawn, and. a mandrel adapted to extend within the tubing as it passes through the die whereby to support the tubing internally, said mandrel being adapted to extend through the die and to project therebeyond a distance greater than the diameter of the mandrel, whereby to support the tube as and after it leaves the die, wherein the mandrel comprises piano wire having hardened end portions extending in and projecting beyond the die.

6. Apparatus for. drawing tubes comprising a. die of tungsten carbide having an opening through which tubing may be drawn, and a mandrel comprising a length -of piano wire adapted to extend within the tubing as? it passes through the die whereby to support the tubing internally, said piano wire mandrel having an 3,091,001 end extending through the die and projecting therebeyond a. distance greater than the diameter of the mandrel whereby to support the tube as and after it leaves the die.

'7. Apparatus as-set forth in claim 6, wherein the die as well as the portions of piano wire mandrel extending therethrough have a pleted coating 01' metallic material.

JULIUS A. KOBBERUP. HOWARD M. THREIKELD. JACK R. KOBBERUP. 

